Wednesday, December 7, 2011

The balanced force technique

The balanced force technique, first described by Roane et al.,is now the most widely taught technique for manipulating handfiles. It is particularly good when negotiating the curved root canal. The technique requires flexible files with non-cutting tips. The file is inserted into the canal until slight resistance is felt and then rotated 60  clockwise to engage the flutes into the dentine. If a greater movement is made, iatrogenic problems can quickly arise. Using light apical finger pressure to hold the file at exactly the same depth in the canal, the file is now rotated through 360  in an anticlockwise direction. The first 60  of this turn cuts off the dentine engaged in the flutes of the file, and the remainder of the movement picks up this dentine in the flutes of the file prior to the next cycle. The amount of apical pressure required to rotate the file anticlockwise is just sufficient to prevent it from winding out of the canal. Watching the rubber stop in relation to the tooth assists in keeping the file steady with no in or out movement. 

If the file is engaged too far into dentine with the first clockwise movement, ie if the turn is greater than 60 , excessive force is applied to the file during the cutting phase, and the file may fracture. The balanced force cycle of movement should be made no more than three times before the file is withdrawn to be cleaned, ideally by pressing it into a sterile sponge. The root canal system should be irrigated copiously before the file is reintroduced. Using this method, curved canals may be prepared to the full working length without producing apical transportation.